As a rule off thumb.,,,,,
Windows7 is very simalar to windows vista in many ways but 7 has been optimised to run on lower power machines such as net books and laptops. However the end result (as far as gamers are concerned) is that this makes win7 an ideal gaming platform as it free's up more system memory for your games!!! win win!!
As such I'd go with the system spec for vista but take away 500mg from the memory spec.
E.g. crysis warhead....
Vista spec - cpu 3.2GHz, Mem 1.5 gig, Hd 2gig, vid card 256mb.
Windows7 - cpu 3.2GHz, Mem 1 gig, Hd 2gig, vid card 256mb.
However we all know system spec's are misleading and are more like bare minemum spec. If you want to play crysis in it's full glory in directx 10 with a...